inbuxa:ProtocolPolicy over JMAP

The switch is now reachable. /get and /set on a server-level singleton,
wired through jmap-proto the way inbuxa:AiLimits is: object, method names,
request and response variants, reference resolution and evaluation.

/set does not write the policy. It hands what was asked to
Server::set_protocol_policy, which applies the locks, moves the listener
objects and opens or closes their sockets, and reports what happened. So
the method cannot drift from what the switch actually does.

Two properties exist for the screen rather than the server. lockedProtocols
serves LP-21's locked set, so the selector renders SMTP and JMAP locked
from what the server says instead of a list the front end carries -- and
unlocking later needs no admin release. wouldClose answers LP-16: exactly
which listeners turning the switch on would close, by name and port, before
anything happens. It is computed against a hypothetical disabled policy, so
it reads the same whichever way the switch is set, and the registry is only
asked when the property was requested.

savedListeners, changedAt, changedBy and both of those are the server's to
say; a client that sets one gets invalidProperties naming it. closeSubmission
is different: locked, not immutable, so it is overruled rather than refused
and the response hands back what was really stored (false). JMAP already has
the place for that, the value beside an updated id.

Permissions reuse SysNetworkListenerGet and SysNetworkListenerUpdate rather
than adding to a schema-generated enum -- the same choice AiLimits made with
the classifier's. It also reads right: this takes listeners away and puts
them back, so whoever may edit a listener may turn the switch.

changedBy stores the account id, not the name, which survives a rename.

Still no screen, no sign-in refusal (LP-6) and no event (LP-8).

crates/jmap-proto/src/request/mod.rs

@@ -116,6 +116,7 @@ pub enum GetRequestMethod {
     MaskedEmail(Box<GetRequest<crate::object::fastmail_masked_email::FastmailMaskedEmail>>),
     DeletedAccount(Box<GetRequest<crate::object::inbuxa_deleted_account::DeletedAccount>>),
     AiLimits(Box<GetRequest<crate::object::inbuxa_ai_limits::AiLimits>>),
+    ProtocolPolicy(Box<GetRequest<crate::object::inbuxa_protocol_policy::ProtocolPolicy>>),
 }
 
 #[derive(Debug)]
@@ -139,6 +140,7 @@ pub enum SetRequestMethod<'x> {
     MaskedEmail(Box<SetRequest<'x, crate::object::fastmail_masked_email::FastmailMaskedEmail>>),
     DeletedAccount(Box<SetRequest<'x, crate::object::inbuxa_deleted_account::DeletedAccount>>),
     AiLimits(Box<SetRequest<'x, crate::object::inbuxa_ai_limits::AiLimits>>),
+    ProtocolPolicy(Box<SetRequest<'x, crate::object::inbuxa_protocol_policy::ProtocolPolicy>>),
 }
 
 #[derive(Debug)]